The invention is based on a fuel supply system for delivering fuel for an internal combustion engine.
Until now, there have been fuel supply systems in which a first fuel pump pumps fuel out of a fuel tank to a second fuel pump via a fuel connection. The second fuel pump in turn pumps the fuel into a pressure line, to which at least one fuel valve is connected. Typically, the number of fuel valves is equal to the number of cylinders of the engine. The fuel tank can be constructed such that the fuel valve injects the fuel directly into a combustion chamber of the engine. In the operation of this fuel supply system, a high pressure in the pressure line leading to the fuel valve is necessary.
The second fuel pump is typically driven mechanically directly by the engine. The second fuel pump typically has a pump body that reciprocates in a pump chamber, and the frequency of the pump body is rigidly coupled with the engine rpm. To enable the pumping quantity of the second fuel pump to be controlled despite the rigid coupling of the pump body with the engine rpm, a control valve that controls the pumping quantity can be provided between the first fuel pump and the second fuel pump; during a compression stroke of the pump body, the control valve allows some of the fuel to flow back out of the pump chamber into the fuel connection between the first fuel pump and the second fuel pump. To prevent vapor bubbles from forming inside the spaces containing the fuel, it is important that the control valve, which monitors the connection from the first fuel pump into the pump chamber of the second fuel pump and controls the flow quantity, not throttle the inflow of fuel into the pump chamber excessively during the intake stroke of the second fuel pump. It is therefore important that the control valve have a sufficiently large flow cross section.
Because the flow cross section must be relatively large, the control valve of the prior art is relatively large overall, and to adjust the flow cross section a large, heavy electromagnet and a large, strong spring are required. Because of the requisite size of the flow cross section, it was not possible until now to construct the control valve in such a way that the control valve switches fast enough so that even at high frequency of the pump body of the second fuel pump, satisfactorily precise open- or closed-loop control, i.e., control or regulation, of the pressure in the pressure line leading to the fuel valves could be obtained.
Another disadvantage is that because of the size of the control valve required until now, a relatively long time elapses until the flow cross section of the control valve has closed completely, so that in this transition time some of the fuel flows at relatively high pressure back out of the pump chamber of the second fuel pump into the fuel connection, which means an undesired energy loss and undesired heating of the fuel.
Despite major effort and expense, it was not possible until now to regulate or control the fuel quantity pumped by the second fuel pump sufficiently precisely, including at high engine rpm, and at the same time to assure that no gas bubbles will form in the second fuel pump and that the second fuel pump will not pump any excess fuel quantity, which means an energy loss and heating of the fuel.
The fuel supply system according to the invention offers the advantage that the control valve can be made relatively small overall, and nevertheless, during the inflow of fuel out of the fuel connection into the pump chamber, there is relatively little flow resistance because of the relatively large flow cross section. This in turn has the advantage that upon the inflow of fuel into the pump chamber, the risk of formation of a gas bubble in the fuel is greatly reduced, despite the use of a relatively small control valve.
Because when the fuel is flowing through the opened control valve out of the pump chamber back in the direction of the fuel connection leading to the first fuel pump, the flow cross section is embodied as relatively small, the advantage is obtained that only a relatively small flow cross section has to be controlled, so that it is possible at relatively little effort or expense to embody the control valve in such a way that the flow cross section can be closed or opened very quickly.
By means of the provisions recited herein, advantageous refinements of and improvements to the fuel supply system are possible.
By the closure of the flow cross section as a function of an engine operating condition, the fuel quantity pumped by the second fuel pump can be controlled or regulated highly precisely in a very simple way and with little dissipation. The control valve embodied according to the invention can be opened and closed especially fast and with precise timing.
If the electromagnet of the adjusting drive that adjusts the valve member while the adjusting body of the adjusting drive is in its unactuated position of repose or in other words a certain time before the adjusting body is to execute its adjusting motion, is supplied variably with current adapted as a function of an engine operating condition and/or of a pressure inside the fuel supply system, in particular a head pressure engaging the valve member, and/or as a function of time, and in particular of the instantaneous position of the pump body and/or as a function of a pump rpm, then because the electromagnet builds up precisely enough force that the adjusting body remains in its position of repose, the advantage is obtained that afterward, to adjust the adjusting body out of its position of repose, only a slight change in the current has to be brought about, which can be done within an extremely short time, so that the adjusting body and thus also the valve member actuated by the adjusting body can be switched over extremely fast into the new intended position.
If the control valve is embodied such that by supplying current to the electromagnet the magnetic force generated adjusts the valve member into a closing position in which the flow cross section of the control valve is closed, then the advantage is obtained that overall current has to be supplied to the electromagnet of the control valve only relatively briefly, since the requisite period of time in which the flow cross section is to be open is usually longer than the period of time in which the flow cross section is to be closed.
If the control valve is embodied such that with waning current or if the current to the electromagnet is switched off the spring counteracting the magnetic force of the electromagnet adjusts the valve member into a closing position, in which the flow cross section is closed, then the advantage is obtained that even there is a functional failure of the electromagnet of the control valve, the second fuel pump can pump the fuel out of the fuel connection into the pressure line leading to the fuel valves.
If the control valve is embodied such that when the fuel flows out of the fuel connection into the pump chamber the valve member can lift away from the adjusting body of the adjusting drive, then the advantage is obtained that only the valve member, which has only relatively little mass, has to be moved, which is advantageously expressed in a rapid response of the valve member to pressure changes. A further advantage is that the adjusting body overall has to cover only a little distance, and nevertheless it is possible for the valve member to cover an overall longer adjustment path.
If the control valve is embodied as a so-called seat valve, then with a relatively short adjustment path of the valve member, a relatively large flow cross section can advantageously be controlled or opened and closed.